This invention relates to an ice harvesting/water chiller machine of the type for producing large quantities of ice and/or chilled water and where the ice may be used for thermal energy storage for cooling.
Thermal energy storage has been used for many years. In the past it was economically feasible with certain classic cooling applications such as churches, theatres, and dairies to utilize the stored cooling effect of small refrigeration systems operated over long periods of time to meet large cooling requirements of short duration. In more recent years, thermal energy storage has been used to take advantage of utility pricing policies. Utilities have instituted time-of-use rate schedules to encourage the shifting of electrical demand to off-peak, low electrical demand periods of the day, periods during which utilities have excess generating capacity. Large cooling requirements are prime candidates for electrical load shifting of this type. By shifting electrical demand to off-peak hours, it is possible to obtain cooling during peak hours at close to off-peak costs.
Hence, as with other ice harvesting machines, the ice harvesting machine of the present invention is used to produce large quantities of ice during off-peak periods when the cost of electricity is relatively low, and store the ice for cooling during peak periods when the cost of electricity is relatively high, thus avoiding use of large amounts of electricity during high cost periods.
Ice harvesting machines are known in the art. U.S. Pat. Nos. 4,622,832, 4,531,380, and 2,113,359 disclose such machines where cold refrigerant is distributed over the outer surfaces of vertical tubes, and ice is formed on the inside of the tubes. Other patents disclose such machines using vertical plate-type heat exchangers for forming the ice. Examples are U.S. Pat. Nos. 4,044,568, 3,566,896 and 2,448,453. U.S. Pat. No. 3,546,896 discloses a "pillowed" plate-type heat exchanger where refrigerant is fed within the heat exchanger and water flows from an upper reservoir down over the outer surfaces.
The ice harvesting/water chiller machine of the present invention represents an improvement over such prior machines in providing a machine that is exceptionally efficient for producing large quantities of ice and/or chilled water utilizing an improved evaporator assembly.
Generally, the machine of the present invention includes a storage tank for collecting and storing ice or chilled water produced by the machine for use such as in room cooling during peak load hours, and a refrigeration system for producing the ice and depositing it into the storage tank. The refrigeration system includes an improved evaporator assembly having a plurality of plate-type heat exchangers oriented vertically in face-to-face, parallel, relation above the tank. Each heat exchanger is of the "pillowed" type formed from multiple plates spot welded together at locations spaced uniformly over substantially the entire heat exchanger. The heat exchanger is then inflated so as to pillow between the spot welds to form interior passages between the plates for the flow of refrigerant therethrough.
The assembly further generally includes a water reservoir above the heat exchangers. Water is distributed from the reservoir downwardly to flow over the outside surfaces of the heat exchangers to effect a substantially even distribution of water over the outside surfaces as it flows downwardly thereover. Cold refrigerant is distributed to the tops of the heat exchangers and cascades downwardly over the inside surfaces through the pillowed passages to effect a substantially even distribution of refrigerant over the inside surfaces as it cascades downwardly thereover. To provide such distribution a tube extends across the top of each heat exchanger. The tube has spaced openings along the tube over substantially the entire width of the heat exchanger. These openings communicate with the interior of the heat exchanger. Cold refrigerant is fed through the tube and distributed through the openings into the interior passages of the heat exchanger and cascades downwardly over the inside surfaces thereof, thus cooling the water as it flows downwardly over the outer surfaces.
After a build up of ice of a predetermined thickness on the outer surfaces of the heat exchangers, hot gas is cycled into the interior passages to release the ice which falls into the storage tank below.
The improved evaporator assembly of the present invention produces an exceptionally uniform build up of ice over substantially the entire outer surfaces of each heat exchanger, and does so at high efficiency due to the uniform flow of both cold refrigerant and water over the heat exchanger surfaces.